Calibration issue

Hi..after calibrating x,y,z axis pretty close...I run file (see attached)..and the part comes out about .75" larger than what was generated in cambam..
not sure what is happening here....

Thanks for any help..
Rick

What size piece gives your 0.75" larger, or is the oversizing pretty consistently the same amount regardless of the size of the item or is it a proportional oversizing (bigger pieces off more smaller pieces off less?

Are you using tool diameter offsets? One possibility would be if you have your CAM program generating the tool path with tool offset, but are also using an additional tool offset in Linuxcnc.

How did you determine your step scaling? Did you calculate it from the drive mechanics, or did you use experimentation? (Measure a feed move and adjust the scale to get the size move you wanted.)

If you used experimentation and the system was loosing steps for some reason, This can give a fairly consistent offset in size variation for each move.

Hi...sorry for delay...thought I submitted response..


So tried smaller piece...yes..less off...

Rechecked calibration (experimentation)...was off a bit...I will keep trying.. I made this machine...used mach 3 for many years...never had a problem that you would not hear motors banging from stall ....maybe here missing steps would be silent....
Thanks for your help!

Rick

If you edit your ini file and set the step_scale to be what you had as steps per in Mach, the scale should be correct. Well same as what you had.

I often prefer to calculate what the step ratios "should" be from screw leads, pinion ratios, encoder counts, and steps/revolution. Rather than relying on how well I can read a tape measure to get the distance moved per step. Do you know the mechanical measurements of the components of your drive system and your motor's step count/rev? .

But if I am going to measure it, I'd set the step scale to something like 1,000 then command a move that is some fairly large even number that still fits in your machine's range of movement.  So if your machine is capable of moving from 0 to 500 with the scale set to 1000, then you'd know that the machine took 500,000 steps to make that move.  Then simply measure the length of that 500k step move.  If that move length were say 20" then divide 500,000/20 to get a scale of 25000 steps/inch.  Generally the longer the move you can make and measure, the more accurate your calculation will be.

Hi...sorry for delay...much distracted here...I am going to follow up on all points..

I have it pretty close now...after I finish a couple things I want to go back and check because it seemed that when I used calibration...changed scale value..then tested by jog and measure...ok..save...then run program...consistently got a substantial difference than the jog test which was at the lame total distance..did same process again without testing by jog and much better..I know sounds voodoish but I will try to replicate later this week..

Thanks so much for your help!!

Rick